The cytochrome P450 3 A subfamily is comprised of four genes CYP3A3, CYP3A4, CYP3A5, and CYP3A7; with CYP3A4 expressed in a majority of adult livers. Recently, CYP3A4 has been identified in enterocytes. Thus, intestinal CYP3A may play an important role in the oral bioavailability of CYP3A substrates such as midazolam, nifedipine,and cyclosporine A. Midazolam is a 1,4 imidazobenzodiazepine that exhibits a lower than expected oral bioavailability assuming that the liver is the sole organ of metabolism. A goal of this study is to determine the contribution of intestinal cytochrome P450 3A to the observed first pass metabolism of midazolam following oral administration using simultaneous intravenous and oral administration of midazolam and a stable isotope. A second goal of the study is to determine if clarithromycin inhibits the metabolism following oral administation at the intestinal or hepatic level.